Causes of Panic Disorder
Factors such as heredity, other biological factors, stressful life events, and thinking in a way that exaggerates relatively normal bodily reactions in catastrophic events are believed to play a role in the onset of panic disorder. Currently, the exact cause or causes of panic disorder are unknown.
Suffocation Alarm Theory
Panic attacks are often associated with rapid, heavy breathing (hyperventilation). This kind of respiration absorbs oxygen quickly for emergency purposes. Some researchers believe that during a panic attack the brain is falsely signaling a shortage of oxygen or an increase in carbon dioxide and setting off a suffocation alarm in a person with a low threshold. Because both excess and shortage of carbon dioxide are associated with panic, most experts suggest that a panic attack may occur in a susceptible person who develops any imbalance of gases in the blood sufficient to cause intense physical sensations.
Lactate Sensitivity Theory
When the chemical sodium lactate is
injected into a subject, it produces the physical symptoms associated with panic. These symptoms precipitate panic itself in about four-fifths of people with panic disorder but only one-fifth of the general population. The muscles of the body produce lactate (in the form of lactic acid) during vigorous exercise. Its presence is a sign that the body is straining to meet oxygen needs. Lactate sensitivity might be a sign of genetic susceptibility to panic attacks. It is often found in otherwise healthy members of the families of people with panic disorder.
Underlying Biological Mechanism
Researchers are looking for evidence for an underlying biological mechanism in panic disorder, resulting from the malfunctioning of a natural alarm system.
The underlying mechanism may involve irregularities in the synthesis and release of norepinephrine (NE), one of the neurotransmitters released by the brain in emergencies. Stimulants that alter NE transmission (including cocaine, amphetamines, and even caffeine) can precipitate panic attacks, and many drugs used to treat panic disorder act in the same pathways.
Other brain systems associated with the disorder make use of serotonin (5-HT) or gamma-aminobutyric acid
Hypersensitivity of receptors for one or more of these neurotransmitters could be one cause of the physiological crisis that results in panic.
In studying the effects of stress on brain activity in animals, Elizabeth Abercrombie, Ph.D. of Rutgers University, found that chronic stress increases release of norepinephrine in the hippocampus of animals subjected to a subsequent acute stressor. Dr. Abercrombie also showed that stressful stimuli result in substantial increases in dopamine in three brain regions believed to be involved in the anxiety response. Dr. Abercrombie is hoping to show how stressful life events in humans translate into disturbances of neurotransmitter systems.
Heredity and Stress Response
The risk of panic disorder is probably influenced by heredity. Identical twins are matched for the disorder at a rate of 30%. The risk for a father, mother, brother, sister, parent, or child is 10% to 20%. About 40% of people with agoraphobia have a close relative with agoraphobia. Relatives of patients with both panic attacks and agoraphobia have the same 10% to 20% risk of panic attacks as the relatives of patients with panic attacks alone, but their risk of agoraphobia may be as much as eight times as high. Phobias are genetically related to panic disorder, but depression and generalized anxiety are not.
Dr. Jerome Kagan of Harvard University believes that shyness and sociability are enduring temperamental traits that have a biological basis. He demonstrated that shy children differed from the outgoing children in their physical (biological) responses to new situations. The shy, inhibited children seemed to have a much higher baseline heart rate and more rapid increase in their pulse in response to the stress of a totally new situation or object than did the outgoing, sociable children, suggesting that they had an overly active stress response. If these biological differences are long-lasting, then the shy children might be more vulnerable (and outgoing children relatively immune) to developing anxiety disorders and stress-related illnesses.
Drs. Biederman and Rosenbaum of Harvard University demonstrated that the children of parents with an anxiety disorder were more likely to be shy and inhibited than were children born to parents without anxiety disorders. More importantly, they found that many of the shy children went on to develop anxiety disorders.